I agree with bay-walker, why would anyone want to use a 2-box on the beach, to begin with? They won't find an object smaller than a soda can. Well ... if you tried really hard, and had very good ears, and got it perfectly centered, maybe an object as small as a playing card or matchbox car. But realistically speaking, soda can size and larger. So .... in-lieu of the normal objective of beach hunting, I can't imagine a need or time to use a 2-box on the beach.
Unless you know of a cache someoe buried on the beach?